Define Computer Virus | Computer Virus Types

In computer, VIRUS stands for the Vital Information Resource Under Seize.

Computer virus contains malicious codes written by hackers/attackers with the intention to hurt or infect other computers.These software programs with malicious code can automatically transferred from one computer to another computer by attaching themselves to files or boot records of disks.

Computer viruses are carried on removal storage devices such as USB Pen Drives or Memory Cards, CD and DVD. They can be also transferred through the network or Internet. 

Computer viruses have similar nature like a natural biological virus. Similar to the natural virus, computer viruses have capability to copy itself and infect a computer including different files stored on a computer.

Viruses can cause a destruction to the entire file system. All the files infected by a virus won’t be loaded or run. In such a case, you would need to reinstall and reload the whole system again. 

Once a virus starts infecting a computer, it duplicates itself a number of times till your computer memory goes down or is eaten up by the virus. This results in the performance of the computer and your computer can freeze or stop. 

Computer viruses can format or erase the system files from the secondary storage devices (Hard Disk Drives) without any user intervention. Hackers also encrypt all the files or content stored in your computer and force you to send a huge amount of money for decryption of those encrypted files. 

In computer history, “Creeper” was the first virus detected on ARPANET, in the early 1970s. Creeper was an experimental self-replicating program written by Bob Thomas at BBN Technologies. 

Other common examples of computer viruses are I Love You, Kill Bill, BRAIN VIRUS, Jerusalem, Y2K, w3perite and so forth.

Different Types of Computer Viruses:

Computer viruses are classified into following different types:

  • Trojan Horse
  • Worm
  • Boot Sector Virus
  • Program or File Virus
  • Multipartite Virus
  • Stealth Virus
  • System Virus

Trojan Horse Virus:

A Trojan Horse virus, also referred to as a Trojan, is a software program with malicious code which is written by hackers to infect the computer system. Trojan Horse is a harm-less, non-self replicating virus. 

Hackers infect a computer using a Trojan Horse virus to perform malicious suspicious activities like upload or download some security or unwanted files. Your passwords and credit card information also can be theft if your computer has been infected by a Trojan virus. 

Some of the malicious activities Trojan Horse can perform on your computer are:

  • Installation of unwanted application or software
  • Downloading or uploading of unwanted files
  • Modification or deletion of files from your computer
  • Keystroke logging
  • Viewing the user’s monitor (screen)
  • Wasting computer storage space
  • Crashing or slowing down your computer
  • Steal your sensitive data


A worm is a self-replicating computer virus which can send copies of itself to other computers connected in a network. Worm is attached to a program or files. 

Worm virus duplicates itself a number of times till your computer memory goes down or is eaten up. As a result, it slows down your computer system.

Boot Sector Virus:

A boot sector virus, also referred to as a boot record virus as well as a partition virus. It is called the boot sector virus because it is designed, developed, and created to destroy the boot sector of disk where MBR (Master Boot Record) is stored. 

It injects the malicious code in the startup records and executable files of your computer which result in boot fails and harm the startup procedure. 

Examples of Boot Sector Virus are Danish Boot, Devel 941, Disk Killer, Golden Gate, Brain Virus and so forth.

Program or File Virus:

A program virus, also referred to as a file virus, is a software program with malicious code that infects other application programs installed on your computer. 

Program virus attach itself to the start or end of any executable files or records, usually with extension .EXE, .COM, .BIN, .DRV and .SYS. Once the program infected by File Virus is executed, it remains present in the RAM even after the  is closed. 

Since the virus is residing in main memory, when we execute another program then the virus attaches itself in the new file from main memory. After then they change the code of executable programs or files on which the virus has been attached. 

Examples of program or file virus are acid rain, alient 298 and Crazy A.

Multipartite Virus:

Multipartite virus is the combination of boot sector virus and program virus. It has combined the features of the boot sector and program virus. 

Thus, multipartite viruses have capability to harm the boot sector of disk as well as programs or files on a computer.

Examples of Multipartite virus are Invader, Flip, Tequila and so forth.

Macro Virus:

Macro virus is a tiny software program which is often written, developed and created in the scripting language for Microsoft Office programs installed on a computer. Macro virus does not infect the program files rather it infects the document, report, sheet, database which has been created using the Microsoft Office programs such as Word, Excel, Access and so forth. 

Micro viruses usually get transmitted onto your computer when you download the certain documents that may contain malicious scripts. 

Logic bomb:

Logic bomb also referred to as a time bomb, which is a piece of code that executes when a specific condition has been satisfied on your computer.

How to protect your computer from virus?

That’s why it is recommended to install Antivirus programs such as Kaspersky, Norton and Quick heal. Such antivirus will prevent downloading the malicious files or documents by scanning them.

Prevention is better than cure so to make your computer free from such virus, you have to regularly scan the hard disk, run full computer scanning to check viruses, and do proper scanning of removable disk such as Pen drive, Memory card, CD/DVD.

Some of the common security measures that can help you to protect your computer from viruses are listed below:

  • You must have a strong authenticity mechanism for your computer.
  • User login password must be strong (hard to guess).
  • Passwords should be changed regularly.
  • Passwords should not be shared with others.
  • Install Antivirus programs such as Kasper sky and Norton.
  • Regularly scan your computer including all the files and removable disks.
  • Never download files from unknown web sources.
  • Never download email attachments sent by unknown senders.
  • Take frequent backup of your files and store them on cloud storage.
  • Never connect your computer to a free Wi-fi network.